Optical reproducing method

ABSTRACT

An optical reproducing method for an optical medium including a disk-like substrate, a spiral or concentric-shaped groove structure along a track formed on the disk-like substrate, the groove structure being wobbled in a radial direction of the optical medium, the track being divided into a plurality of units in the track direction by at least one radial boundary line, at least two adjacent units in the radial direction of the optical medium comprise one zone, and the groove structure included in the respective units within one zone having substantially a same number of wobbling. The method includes irradiating an optical spot on the optical medium, detecting a reflected beam from the optical medium, and reproducing information on the optical medium by sing a signal obtained by the reflected beam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 09/761,571, filedJan. 18, 2001, now U.S. Pat. No. 6,388,987, which is a continuation ofU.S. application Ser. No. 09/350,107, filed Jul. 9, 1999, now U.S. Pat.No. 6,219,331, which is a continuation application of U.S. applicationSer. No. 09/090,310, filed Jun. 4, 1998, now U.S. Patent No. 5,930,228,which is a continuation application of U.S. application Ser. No.08/900,294, filed on Jul. 25, 1997, now U.S. Pat. No. 5,936,933, whichapplication relates to U.S. application Ser. No. 08/863,126, filed onMay 27, 1997, now U.S. Pat. No. 5,953,299, entitled “INFORMATIONRECORDING METHOD AND APPARATUS” by H. Miyamoto et al, and assigned tothe present assignee, based on Japanese Patent Application Nos.08-136189 filed on May 30, 1996 and 09-079587 filed on Mar. 31, 1997,the subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to information recording media, andparticularly to a high-density information recording medium and ahigh-density optical recording medium of which the track width issmaller than a beam spot or a detecting means such as a magnetic head.

Japanese laid-open patent publication No. 6-176404, for example,describes an example of a high-density (narrow track) recording medium.This example uses as a recording medium an optical recording medium inwhich groove portions and land portions are formed on a substrate andinformation recording areas are formed on both of the groove portionsand the land portions. Prepits are formed on a virtual prolonged line ofa boundary portion between the groove portion and the land portion asidentification information of a recording unit (sector), wherebyrecording information is recorded on both of the groove portions and theland portions and identification (address) information indicative of arecording area is handled by the prepits. Also, one prepit commonly usesaddress information for a pair of groove portion and land portion.According to this system, when the recording medium of this system isapplied to a phase change type recording medium and a magneto-opticalrecording medium, information from the adjacent land portion or grooveportion can be prevented from being mixed into the groove portion andthe land portion owing to an interference effect caused within the beamspot (i.e. crosstalk can be cancelled out), and hence the tracks of therecording medium can be narrowed, thereby making a high-densityrecording become possible.

However, in the example according to the related art, inasmuch asinformation indicative of the position on the information recordingmedium is concentrated in the prepit portions and the prepit portionslocated in a discrete fashion, position information cannot be obtainedfrom portions other than the prepit portions. As a consequence, it isdifficult to control a rotational speed of a disk precisely with a highreliability. There is then presented the problem from a reliabilitystandpoint that the recording medium according to the relate art is notpersistent to, in particular, defects or the like.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide an informationrecording medium in which the aforementioned problems can be solved andwhich can be made high in recording density and highly reliable byassigning position information to other portions than prepit portions.

A second object of the present invention is to provide an informationrecording and/or reproducing method in which the aforementioned problemscan be solved and in which information can be recorded and/or reproducedwith a high recording density and with a high reliability by using aninformation recording medium in which position information is assignedto other portions than prepits.

In order to attain the above-mentioned first object, the presentinvention used the means which follow:

(1) In an information recording medium having almost spiral-like orconcentric tracks comprising both of groove portions and a land portionbetween the groove portions, the recording medium is divided into groupsof a plurality of areas in the radius direction, each track is dividedat circular arc recording units having the same central angle arrangedto be radial in the radius direction within each group, identificationinformation indicative of the recording unit is provided in the track atevery recording unit, the each track is divided into groups such that alength of a circular arc-shaped recording unit becomes almost constantbetween the groups, and the groove portion and the land portion arewobbled in the radius direction of the information recording medium.

Thus, position information can be reliably obtained in the recordingportions because the identification information is provided at everyrecording unit, and the groove portions and the land portions, which arethe recording portions, are wobbled. In other words, recordedinformation can be accessed reliably and recording information can bepositioned with a high accuracy. Further, since the recording units arearranged to be positioned in the radius direction of the informationrecording medium, the tracks can be accessed with ease, and a crosstalkcaused between position information of each recording unit can besuppressed to the minimum. Since the tracks are disposed in such amanner that the lengths of the circular arc-shaped portions which arethe recording units become almost the same, the recording densitybecomes approximately uniform. Thus, it becomes possible to efficientlyuse the whole surface of the disk. Furthermore, it is possible tocorrect the displacement of tracking with a high accuracy.

Japanese laid-open patent publication No. 6-243468 describes atechnology in which grooves are wobbled and a linear velocity of a diskis calculated by a wobble cycle detecting circuit, thereby rotating thedisk at a constant linear velocity (CLV).

(2) Wobble cycles and phases of the groove portion and the land portionare uniformly arranged to be radial with respect to the adjacent trackswithin each group, whereby the wobbling between the adjacent tracks canbe reliably reproduced without interference. Also, since the widths ofthe respective tracks become constant, the recording characteristics canbe prevented from being affected.

(3) A constant integral multiple of the cycle at which the grooveportion and the land portion are wobbled is made coincident with thelength of the circular arc-shaped recording unit. Thus, the startingpoint and the ending point of the recording unit can be detectedreliably, and it becomes possible to detect an accurate position in therecording unit. Moreover, since the length of the recording unit and thewobble cycle in which the groove portion and the land portion arewobbled are synchronized with each other, it is possible toautomatically and constantly keep the relative speed of the recordingmedium constant by making the frequency of the wobbling become constant.

(4) The maximum values of the amplitudes of wobbling in which the grooveportion and the land portion are wobbled were selected to be smallerthan one-tenth of the track width. Thus, the influence that is exertedupon the recording and reproducing characteristics by theabove-mentioned wobbling could be suppressed to be less than 1−cos(180/10)=−26 dB, and the influence which affects an S/N (signal-to-noiseratio)(˜20 dB) necessary for the normal recording and/or reproductioncan be suppressed to be negligibly small.

(5) Identification information was formed by prepits which were verysmall concave portions and convex portions disposed in the spacingbetween the groove portion and the land portion. Thus, it becomes easyto mass-produce an information recording medium with identificationinformation previously provided therein by a simple manufacturingprocess such as an injection molding. Therefore, a productivity withwhich an information recording medium is mass-produced can be raised.

(6) Identification information was disposed in an intermediate portionformed between a track and a track adjoining to the former track. Thus,since one identification information can be used by both of the twotracks, identification information assigned to one information area isdoubled, and hence a reliability of the identification information canbe improved. The information tracks in which identification informationis disposed can be discriminated from each other by effectivelyutilizing a difference between the positions of the directions along thetrack. Moreover, since a relationship between the identificationinformation of the adjacent track and the identification information ofthe track falls within a constant range, it becomes possible todiscriminate the track from the identification information of theadjacent track.

(7) The track of the groove portion and the track of the land portionwere disposed at least at one portion of the one circumference of theinformation recording medium in such a way as to be connected from thegroove portion to the land portion or from the land portion to thegroove portion. Thus, since it becomes possible to continuously accessthe tracks from the recording track of the groove portion to therecording track of the land portion, an effective transfer rate ofinformation can be raised. Therefore, it becomes easy to record and/orreproduce successive information such as moving picture information onand/or from the information recording medium.

The present invention used the following means in order to attain theabove-mentioned second object:

(8) The above-mentioned information recording medium was used, and lightwas irradiated on the track. Then, a wobbling signal was detected bydetecting reflected light with at least two split photo detectors, andinformation was recorded in the information recording medium and/orreproduced from the information recording medium by controlling arotational speed of the information recording medium in such a mannerthat the cycle of the detected wobbling signal becomes constant. Thus, arotational speed of the disk-like information recording medium can becontrolled with ease and with a high accuracy in such a manner that ascanning velocity of light on the information recording medium becomesalmost constant.

(9) The above-mentioned information recording medium was used, and lightwas irradiated on the track. Then, a wobbling signal was detected bydetecting reflected light with at least two split photo detectors, andinformation was recorded on the information recording medium by using aclock which was generated in synchronism with the phase of the detectedwobbling signal. Thus, since it becomes easy to make the length of eachrecording unit on the information recording medium become constant, thelengths of extra gaps on the information recording medium can beminimized.

(10) The above-mentioned information recording medium was used, andlight was irradiated on the track. Then, a wobbling signal was detectedby detecting reflected light with at least two split photo detectors,and a displacement of the track was detected by comparing the amplitudesof the wobbling signals obtained from the two photo detectors of thesplit photo detector. Thus, since information can be recorded on theinformation recording medium and/or reproduced from the informationrecording medium while the displacement amount of the track is beingmonitored constantly, a reliability in the positioning servo can beimproved greatly.

(11) The recording medium is an optical disk of a concentric-shaped orspiral-like groove configuration arranged along the tracks. This groovestructure is wobbled in the radius direction of the optical disk. Thetrack of the optical disk is divided into a plurality of recording unitsby radial boundary lines in the track direction. Of the recording unitsthus divided by the radial boundary lines, at least two recording unitsadjoining in the radius direction of the optical disk constitute onezone, and the groove structures included in the respective recordingunits within one zone have almost the same number of the wobbling.

Thus, since the position information can be highly reliably obtainedeven from the recording portions owing to the wobbling, recordedinformation can be accessed reliably. Hence, it becomes possible toaccurately position recorded information on the optical disk. Further,since the recording units are arranged to be radial in the radiusdirection within the group (zone), recorded information among the trackscan be accessed with ease, and a crosstalk between the positioninformation of the respective recording units can be suppressed to theminimum.

The recording unit need not always agree with the length of the sector,and a plurality of sectors of more than two sectors may be collected asthe recording unit. Furthermore, a plurality of recording units may becollected as a logical sector or a logical block used to correct anerror. At any rate, the recording unit herein will be referred to as anarea of almost constant length provided within the optical disk.

(12) The recording medium is an optical disk of a concentric-shaped orspiral-like groove configuration arranged along the tracks. This groovestructure is wobbled in the radius direction of the optical disk. Thetrack of the optical disk is divided into a plurality of recording unitsby radial boundary lines in the track direction. Of the recording unitsthus divided by the radial boundary lines, at least two recording unitswhich are adjoining to each other in the radius direction of the opticaldisk constitute one zone. The optical disk includes a plurality ofzones, and the groove structures included in one recording units withinany zone have almost the same number of the wobbling.

Thus, since the relationship between the information recording unit andthe duration of the wobbling becomes equal on the whole surface of theoptical disk, it becomes possible to control the rotational speed of theoptical disk and to generate the recording clock by using the wobblesignal without switching the wobble signal in the zone. Therefore, adensity within the optical disk can be made almost uniform by theapparatus of the simple configuration, and hence it becomes easy toutilize the whole surface of the optical disk efficiently.

(13) The recording medium is an optical disk having a concentric-shapedor a spiral-like groove configuration, and the groove structure iswobbled in the radius direction of the optical disk. The groovestructure of the optical disk is divided into a plurality of recordingunits in the circumference direction of the optical disk by the radialboundary lines. Of the recording units thus divided by the radialboundary lines, at least two recording units which are adjoining to eachother in the radius direction constitute one zone, and the groovestructures which are adjoining to each other in the radius direction ofthe optical disk have substantially the same wobbling cycle.

Alternatively, there might be used the following means:

(14) The recording medium is an optical disk having a concentric-shapedor a spiral-like groove structure, and the groove structure is wobbledin the radius direction of the optical disk. The groove structure of theoptical disk is divided into a plurality of recording units in thecircumference direction of the optical disk by the radial boundarylines. Of the recording units thus divided by the radial boundary lines,at least two recording units which are adjoining to each other in theradius direction of the optical disk constitute one zone. The groovestructures of the adjacent recording unit areas in the radius directionof the optical disk within one zone have almost the same wobbling cycleand the same number of the wobbling.

Thus, since the position information can be reliably obtained even fromthe recording portion, recorded information on the optical disk can beaccessed highly reliably, and the recorded information can be positionedwith a high accuracy. Furthermore, since the wobbling is arranged to beradial in the radius direction within the group (zone) and the phases ofthe wobbling are the same in the grooves, it becomes easy to access thetracks of the optical disk. Also, it becomes easy to detect the wobblingsignal at a high quality of a signal. Strictly speaking from a theorystandpoint, although this wobbling signal has a cycle proportional tothe position at which the groove is located in the radius directionwithin one zone, the grooves which are close to each other like thegrooves within one zone have almost the same wobbling cycle.Incidentally, the number of the wobbling need not always be limited toan integral number within the recording unit area.

(15) The recording medium is an optical disk having a concentric-shapedor a spiral-like groove structure. The groove structure is wobbled inthe radius direction of the optical disk, and the groove structure ofthe optical disk is divided into a plurality of recording units in thecircumference direction of the optical disk by the radial boundarylines. Of the recording units thus divided by the radial boundary lines,at least two recording units which are adjoining to each other in theradius direction constitute one zone. The optical disk includes aplurality of zones, and the groove structure has almost the samewobbling cycle in the unit areas which are adjoining to each other inthe radius direction of the optical disk within every zone, and also hasthe same number of the wobbling.

Thus, since the relationship between the information recording unit andthe duration of the wobbling cycle becomes equal on the whole surface ofthe optical disk, it becomes possible to control the rotational speed ofthe optical disk and to generate a recording clock by using the wobblingsignal without switching the wobbling signal in the zone. Thus, since adensity within the optical disk can be made almost uniform by theapparatus of the simple configuration, it becomes easy to utilize thewhole surface of the optical disk efficiently.

(16) The recording medium is an optical disk having a concentric-shapedor a spiral-like groove structure. The groove structure is wobbled inthe radius direction of the optical disk, and the track of the opticaldisk is divided into a plurality of recording units in the trackdirection by the radial boundary lines. Of the recording units thusdivided by the radial boundary lines, at least two recording units whichare adjoining to each other in the radius direction of the optical diskconstitute one zone. Central angles corresponding to one period of thewobbling of the groove structure included in the respective recordingunits within one zone are the same, and the starting positions of thewobbling are arranged to be radial in the radius direction of theoptical disk at each recording unit.

Thus, since the wobbling signal between the adjacent tracks can bereliably reproduced without interference and the width of each trackbecomes constant, the recording characteristics can be protected frombeing affected.

(17) The recording medium is an optical disk having a concentric-shapedor a spiral-like groove structure. The groove structure is wobbled inthe radius direction of the optical disk. The track of the optical diskis divided into a plurality of recording units in the circumferencedirection of the optical disk by the radial boundary lines. Of therecording units thus divided by the radial boundary lines, at least tworecording units which are adjoining to each other in the radiusdirection constitute one zone. Assuming that N is one integral numberthat is made common to all of the recording units on the optical disk,then the optical disk includes a plurality of zones, and all wobblecycles included in one recording unit of each zone is set toapproximately 1/N times the length of the recording unit.

Thus, since the relationship between the information recording unit andthe duration of the wobbling cycle becomes equal on the whole surface ofthe optical disk, it becomes possible to control the rotational speed ofthe optical disk and to generate the recording clock by using the wobblesignal without switching the wobble signal depending on the zone, andhence a density within the optical disk can be made almost uniform bythe apparatus of the simple configuration. As a consequence, it becomeseasy to make effective use of the whole surface of the optical diskefficiently. Moreover, since the integral multiple of the wobbling cycleagrees with the length of the recording unit, the phases of the wobblingsignal can be perfectly connected between the adjacent recording unitswithout fractions. Hence, it becomes easy to generate a timing signalsuch as a clock over a consecutive recording unit by using the wobblingsignal. The fact that the wobbling signal is connected without fractionsas described above means that the phases of the wobbling signals arecontinuous between the adjacent recording units, and the wobblingsignals need not always be continuously connected physically.Specifically, although it is possible to use such a wobble structurethat the wobbling signal is dropped out over several cycles at theboundary portion of the recording units, if such dropout portion isinterpolated (compensated for), then the phase of the wobble signal iscontinuously connected in the adjacent recording unit areas.

(18) Identification information was provided at every recording unit.Thus, it becomes easy to access the recording unit on the optical disk.Also, it becomes possible to fix the position of the beam spot at allpositions on the optical disk by combining a signal detected from thewobbling and the identification information. Therefore, a reliabilitywith which information is recorded on the optical disk and/or reproducedfrom the optical disk can be improved. Moreover, an accuracy with whichrecorded information is positioned on the recording medium can beimproved. Thus, a buffer area required when information is recorded onthe recording medium can be reduced. As a consequence, it becomespossible to enlarge a recording capacity of the recording medium.Moreover, even when a part of identification information on the opticaldisk cannot be detected due to a defect or the like, the position of thebeam spot can be identified based on beam spot position informationobtained from the wobbling so that a reliability with which informationis recorded on the optical disk and/or reproduced from the optical diskcan be improved greatly. If the above-mentioned advantage is used, eventhough recording media are not inspected when they are shipped, areliability with which information is recorded on the optical diskand/or reproduced from the optical disk can be maintained so that a costof the recording medium can be reduced considerably. Moreover, since therecording medium is very resistant to smudges, and need not be protectedby some suitable means such as a case. Thus, it becomes possible toprovide an inexpensive recording medium.

(19) The above-mentioned identification information was formed byprepits comprising optical concave or convex portions.

Thus, optical disks can be mass-produced with ease by a replica method,and it becomes possible to provide stable and highly-reliableidentification information which can be prevented from beingdeteriorated.

(20) The recording medium includes information recording areas providedalong the central line of the groove structure and the central line ofthe land structure.

Thus, according to the above-mentioned information recording areas, itbecomes possible to dispose recorded information with a high density,i.e. it is possible to realize a medium of a high density (largecapacity).

(21) Light is irradiated on the recording medium, a wobble signal isdetected by detecting reflected light of the irradiated light by a photodetector, and a recording or reproducing timing signal is obtained byusing the wobble signal.

Thus, since position information is reliably obtained even from therecording portions by the wobbling of the groove portions and the landportions which are served as the recording portions, recordedinformation can be accessed highly reliably, and recorded informationcan be positioned on the recording medium with a high accuracy, i.e.information can be recorded and/or reproduced on and/or from therecording medium highly reliably, and an accuracy with which informationis recorded on the recording medium can be raised.

(22) Light is irradiated on the recording medium, and the wobble signalis detected by detecting reflected light of the irradiated light with aphoto detector. By using the wobble signal, it is possible to obtain astarting or ending timing at which at least any of recorded informationand identification information is recorded on and/or reproduced from therecording medium.

Thus, since timing information can be obtained highly reliably even whena timing at which the recording unit and the identification signal aregenerated is fluctuated because a revolution rate of the optical disk,for example, is not stable due to the wobbling of the groove portionsand the land portions which are served as the recording portions, therecorded information on the optical disk can be accessed highlyreliably. As a consequence, a speed at which recorded information isaccessed can be raised, and it becomes possible to use an inexpensivemotor so that an information recording and/or reproducing apparatus canbe produced inexpensively.

(23) At least one identification information is detected by irradiatingthe recording medium with light. When at least one succeedingidentification information which succeeds the identification informationis detected, the recording area that should be identified by thesucceeding identification information is recorded on or reproduced fromthe recording medium by using either an identification informationdetecting signal indicating that the succeeding identificationinformation is detected or a pseudo-succeeding identificationinformation detecting signal which is generated from a recording orreproducing timing signal obtained from the above-mentioned wobbling ofthe groove portions and the land portions.

Thus, even when the succeeding identification information cannot bedetected due to some causes such as defects or smudges, the recordingarea that should be identified by the succeeding identificationinformation can be accessed by using the signal obtained from thewobbling so that a reliability with which information is recorded on therecording medium and/or reproduced from the recording medium can beincreased greatly.

(24) There is provided a method of recording and/or reproducinginformation in which information is recorded on and/or reproduced from arecording medium by using a timing signal obtained from the wobblinginstead of identification information if the identification informationcannot be detected when the identification information is detected byirradiating light on the recording medium.

Thus, even when the succeeding identification information cannot bedetected due to some causes such as defects or smudges, the recordingarea can be accessed highly reliably by using the wobble signal, andhence a reliability with which information is recorded on and/orreproduced from the recording medium can be improved greatly. Therefore,since the reliability in recording and/or reproducing information onand/or from the recording medium can be maintained high withoutinspecting the recording medium when the recording medium is shipped, itbecomes possible to reduce the cost of the recording mediumconsiderably. Furthermore, since the recording medium becomes veryresistant to the smudges, the recording medium need not be protected bysome suitable means such as a case. Therefore, it becomes possible toprovide a more inexpensive recording medium.

(25) Light is irradiated on the recording medium, and a wobble signal isdetected by detecting reflected light of the irradiated light with aphoto detector. When a recording or reproducing timing signal isgenerated from the wobble signal, at least the portion in which theabove-mentioned identification information is provided can beinterpolated by a signal synchronized with a series ofimmediately-preceding wobble signals.

Thus, the recording and/or reproducing timing signal obtained from thewobble signal is prevented from being deteriorated due to theidentification signal of the identification information portion, andhence the position information from the wobble information can be highlyreliably obtained even at the position located immediately after theidentification information. Specifically, since the area locatedimmediately after the identification information that cannot be detectedcan be accessed highly reliably, it is possible to maintain areliability with which information can be recorded on and/or reproducedfrom the recording medium. Therefore, it becomes possible to carry out areal time recording and/or reproduction and a highly-reliable recordingwithout the dropout of the information at all.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating the manner in which the tracks aredisposed in an information recording medium according to an embodimentof the present invention;

FIG. 2 is a plan view illustrating the manner in which identificationinformation is disposed in the information recording medium according tothe embodiment of the present invention;

FIG. 3 is a plan view illustrating the manner in which identificationinformation is disposed at a track connected portion in the informationrecording medium according to the embodiment of the present invention;

FIG. 4 is a fragmentary perspective view illustrating the informationrecording medium according to the present invention in an enlargedscale;

FIG. 5 is a plan view illustrating the manner in which the dividedgroups are disposed in the information recording medium according to theembodiment of the present invention;

FIG. 6 is a plan view illustrating the manner in which identificationinformation is numbered in the information recording medium according tothe embodiment of the present invention;

FIG. 7 is a block diagram showing an example of a recording and/orreproducing apparatus using the information recording medium accordingto the present invention;

FIG. 8 is a diagram of a waveform of a reproduced signal obtained fromthe information recording medium according to the present invention;

FIG. 9 is a diagram of a waveform of a signal that is used to recordand/or reproduce the information recording medium according to thepresent invention; and

FIGS. 10A through 10D are respectively diagrams used to explain arecording and/or reproducing method using the information recordingmedium according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will hereinafter be described withreference to the accompanying drawings. Reference numerals in the sheetsof drawings should identify the following elements and parts.

Reference numeral 1 denotes a recording unit, reference numeral 2denotes identification information, reference numeral 3 denotes a grooveportion, reference numeral 4 denotes a land portion, reference numeral 5denotes a track switching portion, reference numeral 6 denotes anon-switching portion, reference numeral 7 denotes a beam spot,reference numeral 15 denotes a wobbling, reference numeral 16 denotes aone cycle of wobbling, reference numeral 21 denotes identificationinformation disposed at a first position, reference numeral 22 denotesidentification information disposed at a second position, referencenumeral 23 denotes a prepit, reference numerals 11 and 12 denoterecording units, reference numerals 91, 92, 93 denote grooves, andreference numerals 81, 82 denote information recording portions,respectively.

Embodiment 1: Information Recording Medium

FIG. 5 shows the manner in which tracks and sectors of the informationrecording medium according to the present invention are disposed. Asshown in FIG. 5, a plurality of groups 91, 92 and 93 are disposed in theradius direction of a disk-like recording medium 8. The track 3 iswobbled by a very small amount in the radius direction of the disk-likerecording medium 8. Each track 3 is divided into a plurality of circulararc-like sectors (recording units) 1 arrayed in the radius direction ofthe disk-like recording medium 8. The length of the circular arc-likesector 1 is selected in such a manner that the number of the dividedsectors per circumference of the disk-like recording medium 8 increasesin the groups located at the position of the larger radius so as to makethe length of the circular arc-like sector 1 become almost constantindependently of the groups.

FIG. 1 shows an example of the manner in which tracks are disposedwithin one group of the information recording medium according to thepresent invention. As shown in FIG. 1, within one group, there arealternately located groove portion information tracks 3 having a widthof 0.7 μm and a depth of 60 nm and a land portion information track 4having a width of 0.7 μm. The groove portion information track 3 and theland portion information track 4 are connected to each other by aswitching portion 5. Specifically, the groove portion information track3 is arranged such that it is connected to the adjacent land portioninformation track 4 after one circumference of the track, and the landportion information track 4 is arranged such that it is connected to theadjacent groove portion information track 3 after one circumference ofthe track. Each track is divided into a plurality of circular arc-likerecording units such as sectors, and identification information 2 isdisposed at the head of each of the information recording units 1. Inthis example, the length of the sector is about 8 mm, which correspondsto a user capacity of 2048 bytes. The groove portion information track 3and the land portion information track 4 are wobbled with an amplitudeof about 20 nm in the radius direction of the disk-like recording medium8. A wobble cycle during which the groove portion information 3 and theland portion information track 4 are wobbled in the radius direction wasset to 1/145 of the sector length, i.e. about 55 μm. The ratio of 1:145was selected in such a manner that the wobbling cycle becomes anintegral multiple of the length (channel bit length) of recorded data.According to this arrangement, it becomes easy to generate a recordingclock from the wobbling.

FIGS. 2 and 3 are respectively fragmentary plan views illustratinginformation identification information portions in an enlarged scale.

FIG. 2 schematically shows a portion 6 in which preceding and succeedingtracks of identification information are connected by the groove portioninformation tracks 3 and the land portion information tracks 4. Also,FIG. 3 schematically shows a portion in which preceding and succeedingtracks are connected at the groove portion information tracks 3 and theland portion information tracks 4, i.e. a portion in whichidentification information is disposed such that the positions of thedirections extended along the information tracks are different in theadjacent tracks but agree with the track advanced or delayed by twotracks. As shown in FIG. 2, identification information is disposed to beradial in the radius direction at the two places of the first position21 and the second position 22. The preceding and succeeding tracks areconnected by the groove portion information tracks 3 and the landportion information tracks 4. In this illustrated example of FIG. 2,each identification information corresponds to the recording area of theright-hand side information track. Further, identification informationcorresponding to the right-hand side groove portion information track 3is disposed at the first position 21, and identification informationcorresponding to the land portion information track 4 is disposed at thesecond position 22. Specifically, the positions of the identificationinformation along the information tracks are different from each otherin the adjacent tracks but agree with each other in the tracks advancedor delayed by the two tracks.

In the switching portion 5 of FIG. 3, the preceding and succeedingtracks of identification information are connected to each other in thegroove portion information track 3 and the land portion informationtrack 4. Also in this case, each identification information correspondsto the recording area of the right-hand side information track. As shownin FIG. 3, Identification information corresponding to the right-handside groove portion information track 3 is disposed at the firstposition 21, and identification information corresponding to the landportion information track 4 is disposed at the second position 22.

As a consequence, when the beam spot 7 scans the land portioninformation track 4, only pits of the one side are constantlyreproduced. There is then no risk that a crosstalk occurs from theadjacent track. Therefore, it becomes possible to satisfactorilyreproduce address information from the prepits without crosstalk. Theaddress information at the prepit is recorded by an 8/16(eight-to-sixteen) modulation code (channel bit length is 0.2 μm).

FIG. 4 is a perspective view illustrating the manner in which tracks andidentification information are configured according to the embodiment ofthe present invention, highlighting the manner in which identificationinformation is formed by small concave portions (pits) 23.

According to this embodiment, since the pits 23 are equally disposed onboth sides of the track (land portion or the groove portion), a badinfluence exerted by the pits 23 upon a tracking servo signal can becancelled out. Accordingly, it is possible to suppress a track offset tobe sufficiently small. Further, when the land portion information track4, for example, is reproduced, address information of the first prepitportion 21 and address information of the second prepit portion 22 arereproduced continuously. Therefore, if information is disposed in such afashion that both of the address information of the first prepit portion21 and the address information of the second prepit portion 22 may beintegrated as one address information, then address (track No.), i.e.identification information can be set independently of the land portioninformation track 4 and the groove portion information track 3.Specifically, it becomes possible to discriminate the land portioninformation track 4 and the groove portion information track 3 from eachother by continuously reproducing the address information of the firstprepit portion 21 and the address information of the second prepitportion 22.

FIG. 6 shows concretely an example of the manner in which identificationinformation is numbered. In FIG. 6, there are illustrated theidentification information of the recording area 11 and theidentification information of the recording area 12. In this example,identification information is recorded on and/or reproduced from therecording medium by relatively scanning detection spots from left toright of FIG. 6. A groove portion information track K of the left-handside, for example, is connected to a land portion information track K+1of the right-hand side of the switching portion 5. A land portioninformation track K+1 of the left-hand side is connected to the landportion information track K+1 after one circumference. In this example,identification information of an information recording area 81 of thegroove portion information track K, for example, is N−1+S where Sdenotes a sum of optical recording information units per circumferenceof the track. When the identification information portion 6 of thistrack is reproduced by the beam spot or the like, N−1+2S is reproducedas identification information located at the first position 21, andN−1+S is reproduced as identification information located as the secondposition 22. In this case, if a smaller number is constantly used as arecording area No. in advance, then N−1+S is used as identificationinformation of the information recording area 81 of this groove portioninformation track K. When the land portion information track K−1 isscanned by the beam spot or the like, N−1 is similarly used asidentification information located at the first position 21. At the sametime, it is possible to discriminate the groove portion informationtrack and the land portion information track from each other bydetecting whether the identification information located at the firstposition 21 or the identification information located at the secondposition 22 is used.

When the information track located at the track switching portion 5 isreproduced, a correspondence of identification information and recordedinformation can be judged in exactly the same manner, and also thegroove portion information track and the land portion information trackcan be discriminated from each other in exactly the same way.Accordingly, it is possible to switch the track polarity between thegroove portion information track and the land portion information trackby making effective use of the above-mentioned relationship.

While there are two sets of the first and second identificationinformation portions as described above, the present invention is notlimited thereto, and there may be provided a plurality of sets ofidentification information portions. If there are provided four sets ofidentification information portions, for example, then first and thirdprepit portions are located under the groove portions and second andfourth prepit portions are located above the groove portions. If thenumber of the prepit portions increases, then the information recordingmedium according to the present invention becomes resistant to defectsor the like, and therefore becomes highly-reliable.

Here, a phase change type recording film (GeSbTe) was used as arecording film of this information recording medium. Accordingly, arecording mark is produced in the form of amorphous area.

Embodiment 2: Information Recording and/or Reproducing Method

An example of an information recording and/or reproducing method usingthe recording medium according to the embodiment 1 will be describedwith reference to FIG. 7.

As shown in FIG. 7, the information recording medium 8 according to theembodiment 1 is rotated by a motor 162. A light intensity controlcircuit 171 controls a light generating circuit 131 so that the lightgenerating circuit 131 generates light 122 having a light intensityinstructed by a central control circuit 151. A converging circuit 132converges the light 122 generated from the light generating circuit 131to form a beam spot 7 on the information recording medium 8. Reflectedlight 123 of the light 122 is detected by a photo detecting circuit 133.The photo detecting circuit 133 comprises a plurality of split photodetectors. A wobble detecting circuit 191 reproduces information fromthe information recording medium 8 by using a reproduced signal 130 fromthe split photo detectors of the photo detecting circuit 133. When awobbling of the track on the information recording medium 8 is detected,there is used a differential output among the outputs from the splitphoto detectors of the photo detecting circuit 133. The reason that thedifferential output is utilized is based on such a fact that anintensity distribution of diffracted light from the beam spot is changeddepending on a positional relationship between the beam spot and thetrack. On the basis of the wobble signal detected by the wobbledetecting circuit 191, information indicative of the positionalrelationship between the beam spot and the track and further prepitidentification information, a position control circuit 161 controls theposition of the converging circuit 132 and a rotation frequency of themotor 162. When the position control circuit 161 controls the rotationfrequency of the motor 162, the rotation frequency is controlled in sucha manner that a reproduced wobble signal may have apreviously-determined constant value. If the rotational frequency of themotor 162 is controlled by the position control circuit 161 as describedabove, then the rotational speed of the motor 162 can be automaticallyand properly controlled independently of the groups on the informationrecording medium 8. Also, since this rotation information of the motor162 has one cycle of about 55 μm, the rotation information is very highin density, and it becomes possible to control the rotation of the motor162 with a high accuracy. Furthermore, since this rotation informationis disposed all over one revolution of the disk, even when a part of therotation information is dropped out by some causes such as smudges ordefects, the rotation information can be reproduced from the informationrecording medium 8 with a high accuracy satisfactorily.

Embodiment 3: Information Recording and/or Reproducing Method

A description will now be given on a method of recording and/orreproducing information on and/or from an information recording mediumby generating a clock synchronized with a phase of a wobble signal wheninformation is recorded and/or reproduced. In order to generate theabove-mentioned clock synchronized with the phase of the wobble signal,there is used a PLL (Phase-Locked Loop) circuit. Since this clock isaccurately synchronized with the wobble information of the informationrecording medium, if information is recorded on and/or reproduced fromthe information recording medium by using this clock, then informationcan be recorded on and/or reproduced from the information recordingmedium at a timing perfectly synchronized with the position on theinformation recording medium. Therefore, information can be recorded onand/or reproduced from the information recording medium withoutproviding unnecessary buffer areas on the information recording medium,and it is possible to obtain an information recording medium which ishigh in format efficiency. As a consequence, there can be raised arecording capacity of the information recording medium. Furthermore,since the wobble information (rotation information) is disposed all overone revolution of the disk, even when a part of the wobble informationis dropped out, information can be reproduced from the informationrecording medium with a high reliability satisfactorily.

Embodiment 4: Information Recording Medium

FIG. 5 shows the manner in which the tracks and the sectors of therecording medium according to the embodiment of the present inventionare disposed. As shown in FIG. 5, there are disposed a plurality ofzones (groups) 91, 92, and 93 in the radius direction of the disk-likerecording medium 8 having a diameter of 120 mm. In this example of FIG.5, there are divided 24 zones of which the radiuses are ranging fromabout 24 mm to 58 mm. Accordingly, one zone has a band width of about1.4 mm. The groove portion information track 3 is wobbled by a verysmall amount in the radius direction of the disklike recording medium 8.Each of the groove portion information track 3 is divided into aplurality of circular arc-like sectors (recording units) 1 arrayed inthe radius direction of the disk-like recording medium 8. The length ofthe circular arc-like sector 1 is made almost constant independently ofthe zones (groups) so that the number of the divided sectors percircumference increases in the zone located at the position of thelarger radius. In this embodiment, each track 3 is divided in such amanner that there are provided 17 recording units 1 per circumference inthe zone (inner-most peripheral zone) of the radius of about 25 mm. Thenumber of the divided zones increases one by one in the outer peripheralzone. By using the information recording medium having the groupsdivided in such a manner that the number of the divided groups increasesin the outer peripheral zone as described above, the lengths of therecording units 1 in the inner and outer peripheries of the informationrecording medium 8 can be made almost constant. In other words, thedensity of the rotation information can be made substantially constant,and the surface area (i.e. whole surface) of the information recordingmedium 8 can be used effectively. Moreover, since information can berecorded on and/or reproduced from the information recording medium atthe same rotational speed and with the same recording frequency withineach group, an information recording and/or reproducing apparatus usingthe information recording medium can be simplified in configuration. Itis needless to say that the lengths of the recording units are slightlydifferent in the inside and the outside of each zone.

FIG. 1 shows an example of the manner in which tracks within one groupare disposed in the information recording medium according to thepresent invention. As shown in FIG. 1, there are alternately disposedthe groove portion information tracks 3 having a width of 0.74 μm and adepth of 60 nm and the land portion information tracks 4 having a widthof 0.74 μm. In each zone, there are disposed about 950 groove portioninformation tracks 3 and the land portion information tracks 4 of thesame number as that of the groove portion information track 3. Thegroove portion information track 3 and the land portion informationtrack 4 are connected to each other by the track switching portion 5which is located at one place on one circumference of the disk.Specifically, the groove portion information track 3 is connected to theadjacent land portion information track 4 after one circumference of thetrack, and the land portion information track 4 is connected to theadjacent groove portion information track 3 after one circumference ofthe track. Each track is divided into a plurality of circular arc-likeinformation recording units 1, and the identification information 2 isdisposed at the starting portion of each information recording unit 1.In this example, the length of the information recording unit 1 is about8.5 mm, which corresponds to a user capacity of 2048 bytes.

The groove portion and the land portion are wobbled in the radiusdirection of the information recording medium by a half width amplitudeof about 20 nm. The wobble cycle was set to 1/232 of the sector lengthor about 37 μm. The ratio of 1:232 is set not only within one group(zone) but also in all the recording units 1 on the disk. The ratio of1:232 was selected in such a fashion that the wobble cycle becomes anintegral multiple (in this example, 186 times) of the unit length(channel bit length) of the recorded data. Accordingly, the length ofthe recording unit is equivalent to 232×186=43152 channel bits when itis expressed by the channel bit number. Since the wobble cycle is equalto the integral multiples of the recording channel bit as describedabove, it is possible to easily generate a recording clock bymultiplying the wobble frequency with an integral number. Moreover,since the relationship between the information recording unit 1 and theduration of the wobbling cycle becomes equal over the whole surface ofthe disk, it becomes possible to generate the recording clock by usingthe signal obtained from the wobbling without switching the signal atthe zone. Thus, a density within the disk can be made almost uniform bythe apparatus of the simple configuration, and the whole surface of thedisk can be used efficiently. Furthermore, if the rotational speed ofthe disk is controlled in such a manner that the wobbling frequencybecomes constant, then it becomes possible to make a relative linearvelocity between the beam spot and the information recording mediumalmost constant independently of the position of the informationrecording medium. If the linear velocity is made substantially constantas described above, then information can be recorded on and/orreproduced from the recording medium under the same recording conditionsindependently of the position of the information recording medium. Thus,the recording and reproducing characteristics of the informationrecording medium can be controlled with ease, and hence the recordingapparatus and the information recording medium can be configured withease. Here, since the lengths of the recording areas 1 are slightlydifferent in the inside and the outside of the zone, the duration of thewobble cycle of a reciprocal of an integral number of the recording unitalso is different in the inner and outer peripheries of the zone. Thus,it is needless to say that a linear velocity also is different slightly.However, because central angles formed by the recording units areconstant within the zone, the revolution rate (angular velocity) withinthe zone become constants so that it becomes possible to access theinformation recording medium within the zone at a high speed.

Moreover, since the integral multiple (232 times) of the wobbling cycleagrees with the length of the recording unit 1, the phases of thewobbling signals can be perfectly connected to each other withoutfractions between the adjacent recording units 1. Thus, it is easy togenerate a timing signal such as a clock over the consecutive recordingunits 1 by using the wobbling signal. The fact that the phases of thewobbling signals are perfectly connected to each other without fractionsmeans that the phases of the wobbling signals are made continuousbetween the adjacent recording units 1 but the wobbling signals need notalways be continuous from a physical standpoint. Specifically, theremight be used such an information recording medium in which a wobblingsignal is dropped out at the boundary portion of the recording units 1over several cycles. In that case, if such dropped-out portions areinterpolated, then the phases of the wobbling signals may be connectedbetween the adjacent recording units 1. In actual practice, according tothis embodiment, the identification information composed of prepits isprovided at the starting portion of the recording unit and neither thegroove portion information track 3 nor the land portion informationtrack 4 exists with the result that the wobble signal is not formed atall. That is, the wobble signal is dropped out during about 11.2 cyclesdue to this identification information 2. Accordingly, while there existabout 220.8 wobble signals in actual practice, the length of therecording information unit becomes exactly 232 times the cycle of thewobble signal.

Here, the recording unit in this embodiment need not always agree withthe length of the sector. For example, more than two sectors may beintegrated as one recording unit, and identification information may bedisposed within such integrated recording unit. Moreover, a plurality ofrecording units may be integrated as a logical sector or a logical blocknecessary for correcting errors. At any rate, the recording unit in thisembodiment is referred to as an area of substantially a constant lengthin which identification information is disposed at the starting portionthereof.

FIGS. 2 and 3 are respectively plan views illustrating identificationinformation portions of the information recording medium in an enlargedscale.

FIG. 2 shows a portion 6 in which preceding and succeeding tracks ofidentification information are connected at the groove portions and theland portions. FIG. 3 shows a portion 5 in which preceding andsucceeding tracks are connected at the groove portions and the landportions, i.e. a portion in which the positions at which identificationinformation is arrayed along the information tracks are differentbetween the adjacent tracks but agree with the track advanced or delayedby two tracks. As shown in FIG. 2, identification information isdisposed to be radial at a first position 21 and a second position 22 inthe radius direction of the information recording medium. The precedingand succeeding tracks are connected to each other by the groove portioninformation tracks 3 and the land portion information tracks 4. In thisillustrated example, each identification information corresponds to therecording area of the groove portion information track 3 on theright-hand side of FIG. 2. Further, identification informationcorresponding to the groove portion information track 3 on theright-hand side of FIG. 2 is placed at the first position 21, andidentification information corresponding to the land portion informationtrack 4 is placed at the second position 22. Specifically, the positionsat which identification information is arrayed along the informationtracks are different between the adjacent tracks but agree with thetrack which is advanced or delayed by two tracks.

The wobble signal is of a sine wave shape which begins with the samephase relative to all information tracks. The wobble signal startsimmediately after the identification information portion or starts via afew buffer areas. With this arrangement, if points at which phases ofthe sine-wave wobble signal become zero degree are connected to eachother by the adjacent tracks, then these points are arrayed to be radialso that the track width is never changed by the wobble signal. There isthen presented no risk that the wobble signal will exert a bad influenceupon the recording and reproducing characteristics. If the phases of thewobble signals are not made uniform in each track, then there isproduced a portion in which the track width is modulated by the wobblesignal, thereby resulting in the recording and reproducingcharacteristics being affected considerably. Therefore, as is evidentfrom the above description of the present invention, in order to realizethe present invention, it is very important to make the phases(including polarities) of the wobble signals uniform between theadjacent tracks.

In the track switching portion 5 shown in FIG. 3, the preceding andsucceeding tracks of the identification information are connected toeach other at the groove portion and the land portion. Also in thiscase, each identification information corresponds to the recording areaof the information track on the right-hand side of FIG. 3.Identification information corresponding to the groove portioninformation track 3 on the right-hand side of FIG. 3 is placed at thefirst position 21, and identification information corresponding to theland portion information track 4 on the right-hand side of FIG. 3 isplaced at the second position 22.

Therefore, when the beam spot 21 scans the land portion informationtrack 4, for example, only one pit is constantly reproduced. There isthen no risk that a crosstalk from the adjacent track will occur.Accordingly, it becomes possible to satisfactorily reproduce addressinformation provided at the prepits without crosstalk. In this example,the address information provided at the prepits is recorded on theinformation recording medium by an 8/16 (eight-to-sixteen) modulationcode (channel bit length is 0.2 μm). Accordingly, a shortest pit lengthis about 0.6 μm. From a standpoint of simplifying the configuration ofthe information recording and/or reproducing apparatus, the modulationcode of the prepit portion and the modulation code of the userinformation recording portion should preferably be made the same. Inthis embodiment, the modulation code and the recording linear densityare both made the same with the result that most of the circuit portionsof the information recording and/or reproducing apparatus can be madecommon.

FIG. 4 is a perspective view illustrating the manner in which tracks andidentification information according to this embodiment are configured,highlighting the manner in which identification information is formed bysmall concave portions (pits) 23.

In this embodiment, since the pits 23 are equally disposed on both sidesof the track (the land portion or the groove portion), an influenceexerted upon a tracking servo signal by the pits 23 is cancelled out sothat a track offset can be suppressed to be sufficiently small. Further,when the land portion information track 4 is reproduced, the addressinformation of the first prepit portion 21 and that of the second prepitportion 22 are reproduced continuously. Therefore, if information isdisposed in such a fashion that both of address information areintegrated as one address information, then it is possible to separatelyset address (track No.), i.e. identification information independentlyof the land portion information track 4 and the groove portioninformation track 3. Specifically, if the address information of thefirst prepit portion 21 and the address information of the second prepitportion 22 are reproduced continuously, then it becomes possible todiscriminate the land portion information track 3 and the groove portioninformation track 4 from each other.

FIG. 6 concretely illustrates the example of the manner in whichidentification information is numbered, showing identificationinformation of the recording area 11 and identification information ofthe recording area 12. In this example, information is recorded and/orreproduced while detection spots are relatively scanned from left toright of the information recording medium. As shown in FIG. 6, a grooveportion information track k on the left-hand side is connected to aright-hand side land portion information track K+1. The left-hand sideland portion information track K+1 is connected to this track after onecircumference of the information recording medium. In this example,identification information of an information recording area 81 of thegroove portion information track K is N−1+S where reference letter Sdenotes a sum of optical recording information units per circumferenceof the track. If the identification information portion 6 of this trackis reproduced by the beam spot or the like, then N−1+2S is reproduced asidentification information existing at the first position 21, and N−1+Sis reproduced as identification information existing at the secondposition 22. In this case, if a smaller number is constantly used as arecording area No. in advance, then N−1+S is adopted as identificationinformation of the information recording area 81 of this groove portioninformation track K. When the land portion information track K−1 isscanned, N−1 is adopted as the identification information existing atthe first position 21 similarly. At the same time, by the identificationinformation existing at the first position 21 or the identificationinformation existing at the second position 22, it is possible todiscriminate the groove portion information track 3 and the land portioninformation track 4 from each other.

When the information track placed at the track switching portion 5 isreproduced, the correspondence between the identification informationand the recording area can be detected, and the groove portioninformation track 3 and the land portion information track 4 can bediscriminated from each other in exactly the same manner as thatdescribed above. Therefore, by using this relationship, it is possibleto switch the track polarities of the groove portion information trackand the land portion information track.

While there are provided two sets of the first and second identificationinformation portions as described above in this example, there may beprovided a plurality of sets of identification information portions. Ifthere are provided four sets of identification information portions,then the first and second prepit portions may be located on the lowerside of the groove portion (inside of the radius direction), and thethird and fourth prepit portions may be located on the upper side of thegroove portion (outside of the radius direction). Alternatively, thefirst and third prepit portions may be located on the lower side of thegroove portion, and the second and fourth prepit portions may be locatedon the upper side of the groove portion. The information recordingmedium can be made more resistant to the defects or the like and becomehighly-reliable by increasing the number of the prepit portions.

Here, a phase change type recording film (GeSbTe) was used as arecording film. Accordingly, a recording mark is produced in the form ofan amorphous area.

Embodiment 5: Information Recording and/or Reproducing Method

The manner in which information is recorded on and/or reproduced fromthe information recording medium of the embodiment 4 by the informationrecording and/or reproducing apparatus shown in FIG. 7 will be describedbelow. As shown in FIG. 7, the information recording medium 8 accordingto the embodiment 4 is rotated by the motor 162. The light intensitycontrol means 171 controls the light generating circuit 131 to generatethe light 122 in such a way as to obtain a light intensity instructed bythe central control circuit 151. The converging circuit 132 convergesthe light 122 to form the beam spot 7 on the information recordingmedium 8. The light 12 is detected by using the reflected light 123 fromthe beam spot 7 with the photo detecting circuit 133. The photodetecting circuit 133 comprises a plurality of split photo detectors.The wobble detecting circuit 191 reproduces information from theinformation recording medium 8 by using the reproduced signal 130 fromthe split photo detectors of the photo detecting circuit 133. When thewobble signal of the track on the information recording medium 8 isdetected, there is used a differential output between the outputs fromthe split photo detectors of the photo detecting circuit 133. Thisutilizes the fact that an intensity distribution of diffracted lightfrom the beam spot is changed depending upon a positional relationshipbetween the beam spot and the track. On the basis of the wobble signaldetected by the reproducing means 191, information indicative of thepositional relationship between the beam spot and the track and prepitidentification information, the position control circuit 161 controlsthe position of the converging circuit 132, and also controls therotation frequency of the motor 162. In this case, the position controlcircuit 161 controls the rotation frequency of the motor 162 in such amanner that the frequency of the reproduced wobble signal becomes apreviously-determined constant value. If the rotation frequency of themotor 162 is controlled by the position control circuit 161 as describedabove, then it is possible to automatically control the motor 162independently of the zones on the information recording medium 8 so thatthe motor 162 can be rotated at a proper rotational speed. Also, sincethis rotation information has one cycle of about 37 μm, the rotationinformation is considerably high in density, and it becomes possible tocontrol the rotation of the motor 162 with a high accuracy. Furthermore,since this rotation information is disposed all over one revolution ofthe disk, even when one portion of the rotation information is droppedout due to some causes such as smudges or defects, information can besatisfactorily reproduced from the information recording medium 8 highlyreliably.

FIG. 8 shows examples of a reproduced signal 41 of wobble informationand a reproduced signal 42 of identification information portion. Inthis example, photo detectors which are split at least by a half in theradius direction are used as a detector, and there is obtained adifferential signal between the outputs from the two split photodetectors. Specifically, there was used a detection system that issimilar to a detection system of a push-pull signal used in an ordinarytracking control or the like. However, since the frequency of the wobblesignal and the frequency of the identification information signal arehigher than the band necessary for the tracking servo, there wereprepared an amplifying apparatus and a differential circuit, both ofwhich should be in accordance with the high frequency specification.There were obtained reproduced signals 421, 422, 423 and 424 incorrespondence with the first, second, third and fourth identificationinformation signals 21, 22, 23 and 24. When the beam spot 7 is notoverlapping the prepit 23 of the identification information portion 2,reflected light is equally introduced into the above-mentioned splitphoto detectors so that a reproduced signal (differential signal) outputis almost zero. Whereas, under the condition that the beam spot 7 partlyoverlaps the prepit 23 (see FIG. 2), a distribution of reflected lightfrom the beam spot 7 is largely deviated due to a diffraction effect,and the outputs from the split photo detectors are unbalanced. As aconsequence, there is obtained a large differential signal output.Inasmuch as the direction in which the distribution of reflected lightis deviated at that time is different depending on the positionalrelationship between the beam spot and the pit, the differential outputcorresponding to the identification information portions 21, 22 and thedifferential output corresponding to the identification informationportions 23, 24 are inverted in polarity. Accordingly, if this polarityof the differential outputs is used, then it is possible to determineany one of the groove portion information track and the land portioninformation track in which the beam spot is positioned. Identificationinformation can be obtained when the resulting signal is converted intoa binary signal and then decoded by a follow-up slice circuit (notshown). At that time, since error detection information is added to theidentification information, it is possible to judge whether or notidentification information is detected correctly. Hence, there can beused only correct identification information in a plurality ofidentification information.

The wobble signal is detected in a similar manner. Specifically, sincethe positional relationship between the beam spot and the groove ismodulated by the wobbling signal, there is obtained a signal output 41shown in FIG. 8. However, since an amplitude (track displacement amount:20 nm) of a wobble signal is small relative to the displacement amount(about 0.3 μm) of identification information, the amplitude of thewobble signal becomes smaller in proportion thereto.

An example of the manner in which a timing signal (clock signal) isobtained from the wobble signal thus detected will be described withreference to FIGS. 10A through 10D.

Initially, the reproduced signal 41 shown in FIG. 8 is supplied to alimiter circuit shown in FIG. 10A, in which an identificationinformation is limited in amplitude. Then, by using the bandpass filtershown in FIG. 10B, only a signal having a component synchronized withthe wobble signal is extracted from the reproduced signal. Then, theresulting signal is converted into a binary signal by a comparator shownin FIG. 10C, and eventually, there is obtained the clock signal by usinga phase-locked loop (PLL) comprising a phase comparator, a filtercircuit, a VCO (voltage-controlled oscillator) and a divide-by-186circuit as shown in FIG. 10D. At that time, a filter characteristic usedin the PLL is set to be sufficiently lower than the frequencycorresponding to 11.2 wobble cycles in this example in such a mannerthat the clock signal may be prevented from being affected by adropped-out portion (identification information portion) of the wobblesignal. In this embodiment, since the frequency of the wobble signalbecomes 160 kHz, the frequency band of the PLL is set to about 2 kHz.This frequency should preferably be set to be larger than a frequency(about 700 Hz) corresponding to the length of the recording unit from astandpoint of a high-speed accessing.

In this way, there was obtained the clock signal that was synchronizedwith the wobble signal. A method of recording and/or reproducinginformation on and/or from the information recording medium by usingthis clock signal and identification information will be describedbelow.

FIG. 9 is a timing chart used to explain the manner in which informationis recorded on and/or reproduced from the information recording medium.In FIG. 9, reference letters (a), (b), (c), and (d) denote anidentification information detecting signal, a wobble signal, a clocksignal, and a recording and reproducing timing signal, respectively. Theidentification information detecting signal is a signal indicating thatidentification information is detected normally. It is customary thatthe recording unit areas that should be recorded and/or reproduced arediscriminated from each other based on this identification informationdetecting signal and that the recording and/or reproducing timing can becontrolled. According to the present invention, when the identificationinformation could not be normally detected as shown in FIG. 9 (crosseson (a) in FIG. 9 show that identification information could not bedetected normally), it is possible to obtain the recording andreproducing timing signal instead of the identification informationdetecting signal by counting the clock signal obtained from the wobblesignal based on the final identification information that was detectednormally. According to this arrangement, even when identificationinformation cannot be detected normally, there can be obtained therecording and reproducing timing signal. Also, since this recording andreproducing timing signal is generated from the wobble signalsynchronized with the information recording medium, even if there is anerror such as a rotational speed of the information recording medium,the recording and reproducing timing signal can be obtained accurately.Furthermore, even when a plurality of identification information cannotbe detected continuously, there is no risk that errors will beaccumulated. Therefore, it becomes possible to configure an informationrecording and/or reproducing apparatus which can greatly allow errors ofidentification information itself.

If the signal detected from the above-mentioned wobble signal and theidentification information are combined as described above, then itbecomes possible to identify the position of the beam spot at allpositions on the disk. Thus, information can be recorded on and/orreproduced from the information recording medium highly reliably. Withthe above-mentioned advantage, even if the information recording mediumis not inspected at al when the information recording medium is shipped,it becomes possible to maintain the recording and/or reproduction highlyreliable, thereby making it possible to reduce the cost of theinformation recording medium considerably. Furthermore, since theinformation recording medium becomes very resistant to smudges, theinformation recording medium need not be protected from the smudges bysome suitable means such as a case. Therefore, it becomes possible toprovide an inexpensive information recording medium.

According to the aforementioned first to fifth embodiments of thepresent invention, since information can be recorded on and/orreproduced from the information recording medium highly reliably, evenif the information recording medium is not inspected at all when theinformation recording media are shipped, a high reliability with whichinformation is recorded on and/or reproduced from the informationrecording medium can be maintained, thereby making it possible to reducethe cost of the information recording medium considerably. Moreover,since the information recording medium according to the presentinvention becomes very resistant to smudges, the information recordingmedium need not be protected from the smudges by some suitable meanssuch as a case. Therefore, it becomes possible to provide an inexpensiveinformation recording medium.

Further, since the recording units are arrayed to be radial in theradius direction of the information recording medium, the tracks can beaccessed with ease, and a crosstalk between position information ofrespective recording units can be suppressed to the minimum.

Moreover, since the recording units are disposed in such a manner thatthe lengths of the circular arc-shaped portions which are the recordingunits are made almost the same, a recording density becomessubstantially uniform within the disk, and hence it becomes possible touse the whole surface of the disk efficiently.

Moreover, the starting point and the ending point of the recording unitcan be reliably detected by using the wobble cycle, and it becomespossible to detect the accurate position in the recording unit. Also,since the length of the recording unit and the wobble cycle areperfectly synchronized with each other, by making the wobble frequencybecome constant, it is possible to automatically control the rotationalspeed of the information recording medium in such a fashion that therelative velocity of the information recording medium becomes almostconstant.

Further, since it becomes easy to make the length of each recording uniton the information recording medium become constant, the length of theextra gaps on the information recording medium can be minimized.

Furthermore, since it is possible to record and/or reproduce informationon and/or from the information recording medium while monitoring thedisplacement amount of the track, a reliability with which thepositioning servo is effected can be improved greatly.

According to the present invention, since the identification informationis provided at every recording unit and the position information can bereliably obtained from the recording portion owing to the wobbles of thegroove portion and the land portion, the recorded information can beaccessed reliably and the recording information can be positioned on theinformation recording medium with a high accuracy.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments and that various changes andmodifications can be effected therein by one skilled in the art withoutdeparting from the spirit or scope of the invention as defined in theappended claims.

What is claimed is:
 1. An optical reproducing method for an opticalmedium including a disk-like substrate, a spiral or concentric-shapedgroove structure along a track formed on the disk-like substrate, thegroove structure being wobbled in a radial direction of the opticalmedium, the track being divided into a plurality of units in the trackdirection by at least one radial boundary line formed by a dropoutportion, identification information is disposed in the track at a headof each recording unit at the dropout portion, the medium being dividedinto a plurality of zones in a radial direction, a length of a circulararc being substantially the same between the zones in a circumferentialdirection, at least two adjacent units in the radial direction of theoptical medium comprise one zone, and the groove structure included inthe respective units within any zone having substantially a same numberof wobbling, the method comprising the steps of: irradiating an opticalspot on the optical medium; detecting a reflected beam from the opticalmedium; and reproducing information on the optical medium by using asignal obtained by the reflected beam.
 2. An optical reproducing methodfor an optical medium including a disk-like substrate, a spiral orconcentric-shaped groove structure along a track formed on the disk-likesubstrate, the groove structure being wobbled in a radial direction ofthe optical medium, the track being divided into a plurality of units inthe track direction by at least one radial boundary line formed by adropout portion, identification information is disposed in the track ata head of each recording unit at the dropout portion, the medium beingdivided into a plurality of zones in a radial direction, a length of acircular arc being substantially the same between the zones in acircumferential direction, at least two adjacent units in the radialdirection of the optical medium comprise one zone, and the groovestructure which is adjacent to each other in the radial direction of theoptical medium within any zone having substantially the same wobblingcycle, the method comprising the steps of: irradiating an optical spoton the optical medium; detecting a reflected beam from the opticalmedium; and reproducing information on the optical medium by using asignal obtained by the reflected beam.